Interlaced line method



Patented Dec. 31, 1940 1 UNITED STATES PATENT orrlce.

2.227.023 INTERIACED LINE METHOD Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc., a corj poration of New York Application October 5, 1937 Serial No. 167,347

In Germany October 26, 1936 7 Claims.

It is known that an image transmitter according to the interlaced line method exhibits as a frequent fault the effect that the lines of the second group are not situated exactly in the middle between the lines of the first group. Thisinterference is referred to in the following as displacement. The eye is so sensitive to this fault that it already perceives a displacement of approximately 1% of the line spacing. In the case of a greater fault .the impression is that of an image having half the number of lines. It is also known that in the interlaced line method, when an odd number of lines is used, displacement always occurs when the long frame synchronizing impulses have not been completely separated from the short line synchronizing impulses. The requirement for. separation is to be understood, as the frame synchronizing impulse of the first scanning group is synchronous with a line impulse, whilst that of the second group must be situated exactly in the middle between two line impulses and may readily be jammed by the adjacent line impulses. Different remedies against this fault have been proposed.

According to the invention the requisite independence of both groups of synchronisation signals is accomplished by the fact that the line synchronising impulses are suppressed during and short time before each frame synchronising impulse.

Further objects of the invention may be best understood by reference to the following description taken in connection with the accompanying drawing, in which Figs. 1 and 3 show diagrams of connections according to the invention, whilst Figs. 2 and 4 are oscillograms of impulses. The practical embodiment of the method is illustrated in Fig. 1. In the same I is the generator 40 for the line impulses, 2 the generator for the frame change impulses. The relative phase of both is secured in a known manner, e. g. by frequency multiplication or by producing the impulses by the same rotating disc. According to the invention there is inserted in the connection between the generator I and a tube 5 modulating the transmitter an interrupter 3 which is controlled by the frame change impulses. The duration of the latter impulses is reducedby a de- 50 vice 4, and then the impulses are conducted also to the mixing tube 5. This way it is accomplished that the interruption of the line impulsesendures for a longer period than the transmission of the frame impulse as shown in the oscillogram of 55 Fig. 2.

In Fig. 2 the line impulses are shown at 6, the frame impulses as produced by 2 are shown at 1, andthe frame synchronising impulses as shortened by 4 are shown at l 0. The line impulsesareinterrupted during theinterval 8. After a certain "5 time 9 the frame synchronizing impulse I0 is transmitted with the same amplitude 6 as previously the line impulses. The signal Ill. endures for a few line periods dependent on the corre- F sponding standard of transmission. After termination of the frame impulse and a second waiting time H, the line signals return to their original intensity. Ina modification of the method the waiting period ll may also be omitted as being not absolutely essential.

V The interruption ofthe line impulses may be caused by'a derivation of the frame impulse which is advanced in phaseby the time 9. In thepractical embodiment, however, a phase advance is not so simpleto be produced, and a method producing the interruption in acordance with Fig. 2

as described in the following is preferable.

In Fig. 3 the line impulse transmitter I and the interrupter 3 are united in a single tube 2 I. This is,'of course, a possible simplified embodiment of 5. the idea according to the invention. An oscil latory circuit I2 is excited by the line frequency generator 13. Its terminals are applied to the two control grids of the pentode 2i, whilst the middle of the circuit coil is earthed. The two =.,3. grids accordingly would oscillate in phase opposition, if not a phase shifting device consisting'of condenser l4 and resistance 1 5 would be provided. The tube 2| is so biassed that a constant anode if both gridsare controlled by the same oscillation with opposite phase, the anode current is suppressed continually. Only, if at both grids the phase opposition is not complete because of the phase shifting device l4/ l5, in a time corresponding to the phase shifting during each period the anode current flows. Thus it-is obtainedthat the tube 2|. is conductive but for a short fraction of the period of I3, adjustable by Ill/l5, and generates at the anode resistance l5 line impulses of any desired length. An exactly corresponding system produces from the frame synchronizingfrequency generator II, for example from the lighting mains, the frame synchronizing impulses at the anode resistance l8 of the pentode 22. These impulses are first employed for interrupting the sequence of the line impulses. They are coupled in-full intensity with the first or second grid of the tube 2|. The coupling takes place by way of a condenser l9 anda series resistance 28 of suitable dimensions. The actual frame change impulse is tapped on the potentiometer 28. By this division of the voltage there is solved in accordance with the invention the problem of causing the interruption to endure longer than the signal transmission. In this connection reference is made to Fi 4.

In Fig. 4 there is represented the time curve form of the frame change impulse such as produced by tube 22 It is like every impulse with limited width of the frequency band, similar to a resonance curve, i. e., is wider at the base then at the half-value. Sfia may be the form of the impulse when having an amplitude of 10 V., whilst 36b shows the same impulse after reduction to 2.5 V. It is to be seen from Fig. 4 that when using these two impulses for blocking a grid with a blocking potential 3! the interruption of the appertaining emissive current in the case 301) endures for a shorter period than in the case a.

The two periods are designated Ta and Tb in Fig. 4. It can accordingly be accomplished by the potentiometer 98 (Fig. 3) that the frame change impulse does not occur until the line impulses interruption has endured for a certain length of time, and that it ceases long before the line impulses again commence. The same effect may, of course, also be obtained by raising the grid bias of 'the blocking tube.

The mixing and modulating tube 5 in Fig, 3 is also a pentode, the outermost and innermost control grids of which are employed for interrupting a constant emission current, in the one case by the line signals and in the other case by the frame change signals. This way it is accomplished that the amplitude with which the two groups of signals are issued is equal in both cases.

The amplitude is determined by selective elimination of a constant emission current of the tube 5 down to zero in both cases.

( In this way. there is also performed at the same time an effective trimming of possible instability of amplitude, as

' the emission current is unable to drop below zero.

Care is taken that even the weakest impulses of the control generators are sufiiciently powerful to reduce the emission current fully to zero.

It is to be readily deduced from the above that embodiments of the idea according to the invention'other than those particularly set forth in Fig. 3 are possible.

, I claim:

1. A television transmitting system including means for generating push-pull voltage variations of the horizontal scanning deflection frequency, a discharge tube having a cathode, a pair of control electrodes and an output electrode, means for applying the push-pull voltage variations to the of phase relationship to the control electrodes of said second discharge tube to produce impulses having a predetermined duration, means for coupling the output electrode of said second discharge tube to one of the control electrodes of said first named discharge tube whereby the pro- .duction of the horizontal synchronizing signals is discontinued throughout the duration of the produced impulses, means for decreasing the duration of the produced impulses at a predetermined intensity level to produce vertical synchronizing signals, and means for combining the produced horizontal and vertical synchronizing signals.

2. A television transmitting system including means for generating voltage variations of the horizontal deflection frequency, a discharge tube having a cathode, a pair of control electrodes and an output electrode, means for applying the voltage variations to the control electrodes in substantially out of phase relationship to produce relatively short horizontal synchronizing signals, means for generating voltage variations at the vertical deflection frequency, a second discharge tube having a cathode, a pair of control electrodes and an output electrode, means for applying the generated voltage variations in substantially out of phase relationship to the control electrodes of said second discharge tube to produce impulses having a predetermined duration, means for coupling the output electrode of said second discharge tube to oneof the control electrodes of said first named discharge tube whereby the production of the horizontal synchronizing signals is suppressed throughout substantially the entire duration of the produced impulses, means for decreasing the amplitude and duration of the produced impulses to produce vertical synchronizing signals, and means for combining the produced 0 horizontal and the produced vertical synchronizing signals.

3. A television transmitting system including means for producing short horizontal deflection synchronizing signals, said means including a discharge tube having a cathode, a control electrode and ananode, means for producing impulses of a predetermined duration at the vertical deflection frequency, said means including .a second discharge tube having a cathode, a control electrode and an output electrode, means including a condenser for coupling the output electrode .of said second discharge tube to the control electrode of said first discharge tube whereby the production of horizontal deflection synchronizing signals is suppressed throughout substantially the duration of the produced impulsesfand means for decreasing the amplitude of the impulses and accordingly the duration of the impulses at a predetermined amplitude level to produce vertical signals.

4. A television transmitting system including means for producing short line synchronizing signals, said means including a discharge tube having a cathode, a control electrode and an deflection synchronizing discharge tube to the control electrode of said first discharge tube whereby the production of line synchronizing signals is suppressed throughout substantially the duration of the produced impulses, means for decreasing the amplitude of the impulses and accordingly the duration of the impulses at a predetermined amplitude level to produce frame synchronizing signals, and

means including a third discharge tube for combining the produced frame synchronizing signals and the unsuppressed line synchronizing signals.

5. A television transmitting system including means for generating voltage variations at line I deflection frequency, means for producing short line synchronizing signals from the generated voltage variations, means for generating voltage variations at frame deflection frequency, means for producing impulses from the generated voltage variations, means for coupling the impulse producing means to the line synchronizing signal producing means, to discontinue the production of line synchronizing signals throughout substantially the entire duration of the produced impulses, means for decreasing the duration of the impulses to a predetermined amount at a predetermined intensity level to produce frame synchronizing signals, and means for combining the produced line and frame synchronizing signals. i

6. A television transmitting system including means for producing short line synchronizing signals, means for producing impulses corresponding to the frame deflection frequency, means for coupling the impulse producing means to the line synchronizing signal producing means to suppress the production of the line synchronizing signals throughout substantially the entire duration of the produced signals, means for decreasing the amplitude of the impulses and accordingly the duration of the impulses at a predetermined amplitude level to produce frame synchronizing signals, and means for combining the produced line and frame synchronizing signals.

7. A television transmitting system including a generator for producing voltage variations at a predetermined relatively rapid rate, means for producing short synchronizing signals at the predetermined rapid rate from the generated voltage variations, a generator for producing voltage variations at a predetermined relatively slow rate, means for producing impulses at the predetermined slow rate from the generated voltage variations, means for coupling said last named means to said first named means to sup-- press the production of the short synchronizing signals at the rapid rate throughout substantially the duration of the impulses produced at the slow rate, means for decreasing the amplitude of the slow rate impulses and accordingly the duration of the impulses at a predetermined amplitude level to produce synchronizing signals at the slow rate, and means for combining the produced slow rate synchronizing signals and the produced rapid rate synchronizing signals.

.KURT SCHLESINGER. 

